1. Technical Field
The present application relates generally to power conversion and, in particular, to components, systems and methods for converting DC voltage and for generating variable frequency AC voltage from a DC voltage source.
2. Background of the Technology
According to one embodiment, a full-bridge (FB) parallel load resonant (PLR) converter is provided which operates in discontinuous conduction mode (DCM). References to parallel load resonant (PLR) converters can be found in the literature. The basic principle associated with the operation of PLR converter is to utilize the natural resonance of an L-C circuit for energy conversion. Current flowing through the device can be controlled using transistors arranged in various known topologies to regulate the cycles of a resonant waveform. The sinusoidal nature of a resonant waveform has the distinct advantage of allowing for zero current and/or zero voltage switching, which greatly reduces switching losses when compared to traditional pulse width modulation (PWM) techniques. Because “pulse width” is determined by the resonant frequency, voltage regulation is attained via frequency modulation.
Examples of PLR circuits are disclosed in U.S. Pat. Nos. 6,229,718 and 6,020,688, which patents are incorporated herein by reference. These circuits are used mostly in low power applications such as inverters for fluorescent lamp ballast. High efficiency, low voltage, wide load variation resonant converters have also been disclosed [1]. See also U.S. Pat. No. 6,483,731, which is incorporated herein by reference in its entirety. These resonant converters employ a multi-voltage resonant secondary to boost the output voltage.
According to further embodiments, also provided is a power inversion system and modulation techniques for use therewith wherein the system comprises a six-pulse inverter and a full-bridge (FB) parallel load resonant (PLR) converter operating in discontinuous conduction mode (DCM). DC-AC inverters are disclosed in U.S. Pat. Nos. 4,466,070; 4,862,342; 5,774,351; 5,889,668; and 6,519,168. AC-AC converters are disclosed in U.S. Pat. Nos. 4,942,511; 5,010,471; 5,270,914; and 6,839,249. In addition, switch-mode DC-AC inverters with a DC link are disclosed in references [2] and [3] and switch-mode DC-AC inverters with a high-frequency AC link and pulse width modulated (PWM) cycloconverters are disclosed in references [4-6] as well as in U.S. Pat. No. 6,700,803. Cycloconverters are systems that directly convert a higher frequency ac voltage to a lower frequency ac voltage. The inverters disclosed in these references generally involve square-wave bipolar or unipolar pulses with durations that are continuously variable. An objective of the methods disclosed in these references “ . . . [to] produce exactly the same waveforms as conventional PWM, while supporting HF links” [5]. Also, switch-mode DC-AC inverters with a high-frequency AC link and pulse width modulated (PWM) cycloconverters are disclosed in references [7-9]. The inverters described in these references invariably involve the rectification and impulse excitation of a low-pass filter with integral half-cycle sinusoidal, or quasi sinusoidal, voltages originating from a source of high-frequency AC voltage (meaning a waveform with zero average value which is transformable by a high-frequency transformer).
There still exists a need for improved power converters, particularly for conversion of low voltage DC power sources.